Fire fighting pump and its operating methods

ABSTRACT

A fire fighting pump and operation thereof and a fire fighting system and a fire engine, wherein the pump includes a housing, a motor mounted inside the housing and two or more stages of series-connected impeller assemblies. A water inlet is provided on the housing between the motor and the impeller assemblies. The impeller assemblies are mounted on the impeller shaft coaxially and in series with each other. The impeller shaft is fixed on the motor shaft or is coaxial with the latter. The impeller assembly includes a thruster, an impeller, an end cover and a retaining ring on the periphery of the thruster and the impeller, and those four elements are installed in turn. Several first blades are provided in the thruster and several second blades which correspond with the first blades in amount and location are provided in the impeller.

BACKGROUND TECHNOLOGY

(a) Field of the Invention

This invention involves in a kind of water pump and its operating methods, especially in a kind of submersible water pump for the use of forest fire fighting and its operating methods.

(b) Description of the Prior Art

For mountainous landfomms, since forest area has complicated landforms, steep and difficult terrains, luxuriant bushes and grasses and rich vegetations, once there is a forest fire that is strong and spreads quickly, it is very difficult and dangerous to put out the fire with wind extinguishing machines, No. 2 tools, extinguishing bombs and back-type extinguishing gun 34, and especially, it is to put out tree top fire, mountain top fire, high strong fire line, it is impossible to use ordinary tools mentioned above to put out such fire.

Water can put out the fire, furthermore, it is a kind of the most ordinary, effective and cheapest natural extinguishing agent. So it is the first choice to use water to put out the forest fire in many forest-developed countries. Some places with relatively fine economic conditions have taken the lead to use water pump, water vehicle and back-type water gun 34 to extinguish the fire. But fire fighting water source is restricted by high and steep fire site and relatively far distance. Since back-type water gun 34 is restricted by heavy load and no continuous water supply at the fire site, so it is usually to use it to clear up the fire site, it is hard to use it for effectively controlling the fire line, especially for controlling a high strength fire line. Water vehicle has a high cost and is limited by landform, and it is unsuitable for some places where are inaccessible for vehicles.

Existing fire fighting pumps are usually driven by motors by means of belt wheels, with small lifts. In order to realize a certain high lift, it is usually to place a water pump at a certain height to gradually pump water to the required height through series-mounted multiple-stage water pumps. Currently, such application is featured by “multiple-stage connection and infinite water supply” of the water pump, on one hand, it always leads to a dead pump due to empty water hose 33 since there is unbalanced pumping water pressure between pumps, so it usually can neither transmit water to the fire line and nor bring water distinguishing effect into full play, on other hand, it increases cost and transportation difficulties, and especially, when it needs to install several water pumps at different heights and places, installation time is long. For some places with a complicated landform, it may be impossible to install them. Because of long installation time, extinguishing time will be extended and extinguishing operation will become more difficult.

When forest fire occurs at forest mountains, since the mountain is high and steep, road is not accessible and water source is difficult, to put out a forest fire with water doesn't need a big water flow, but it needs to transmit water with long distance and high lift. Therefore, forest fire fighting pump should introduce equipments with relatively low water flow, relatively high lift, relatively light weight and relatively small volume, so as to facilitate carrying and operation at hill area, and it shall not use fire fighting pump equipments for urban use with relatively big water flow, relatively low lift and relative big size and heavy weight.

First, existing fire fighting pump lacks full knowledge on forest fire fighting with water, it doesn't get ride of the wrong field, which forest fire fighting with water also needs a big water flow, high water pressure and long spraying distance; second, study on application idea and pattern of forest fire fighting with water is not sufficient. Forest fire spreading features decide fire line's dynamic feature, thus leading fire area to continue expanding and fire line to extend. Therefore, it lacks an application pattern of effective “dividing forces for encircling and making breakthroughs at several points”. Third, we cannot fetch water everywhere. Under specific forest conditions, if we want to put out a fire with water, we should try to get, transmit and guarantee a water source first. The current water pump cannot meet the need of small-caliber water hose 33 for high lift, long distance, high pressure-proof, fast laying and flexible water distribution to put out a forest fire.

Now, there is a kind of submersible water pump for deep well operation, e.g. patent number 01271640.5, a submersible water pump includes a housing, a motor fitted inside the housing, and a bush in which multiple-stage impellers are installed. On the top of the motor is an end cover while a bearing seat is on its low part. Impellers are installed on the impeller shaft in series. Impeller shaft is connected with the motor shaft by means of a coupling while a water inlet is provided on the housing between motor and impellers. As compared with a submersible water pump driven by a belt wheel of a motor, a submersible water pump of such structure is featured by small volume, big pressure, high lift and simple installation. Since the existing submersible water pump can only use the centrifugal force of the multiple-stage impellers to increase the pressure, so the increased pressure is limited and lift cannot meet the need of fire fighting, therefore, it is usually used for deep well operation, it is not used as a fire fighting pump. The operating methods of current water pump is that only the impellers rotate, but without a thruster, so such kind operating methods of existing submersible water pump cannot form a helical separation propelling mode to her increase the water pressure, as a result, the lift and water transmitting distance cannot meet the need for fire fighting, furthermore, the existing submersible water pump is not yet used for fire fighting, and especially for forest fire fighting.

SUMMARY OF THE INVENTION Invention Contents

The first purpose of this invention aims at providing a kind of fire fighting pump to meet fire fighting need through heightening the lift by means of increasing pressure between the impeller assemblies of the submersible water pump.

The second purpose of this invention aims at providing operating methods of a fire fighting pump with long distance, high lift and strong pressure resistance.

To realize this invention is a kind of fire fighting pump that includes a pump housing, a motor installed inside the pump housing and series-mounted two-stage or over two-stage impeller assemblies installed inside the cylindrical cavity of the pump housing. Pump housing is equipped with a water inlet between the motor and the impeller assemblies that are coaxially mounted on the impeller shaft or with the motor shaft. Impeller shaft is fixed on the motor shaft. The impeller assembly includes a thruster, impellers, an end cover and retaining rings. At the center of the end cover is equipped with the first vent. The thruster includes the central shaft, 3 or more than 3 first blades, the first hub and the second hub, the first blade is fitted between the first hub and the second hub; 3 or more than 3 first division grooves are formed among the first hub, first blades and the second hub. Inside the central shaft is provided with a second vent that matches the impeller shaft. The thruster is fixed on the impeller shaft through the second vent. Impellers include the second blades whose number is the same as those of the first blades, the third hub and the fourth hub. The position of the second blade corresponds with position of the first blade. The second blades are placed between the third hub and the fourth hub. The second division grooves are formed among the third hub, the second blades and the fourth hub, whose number is the same as those of the first division grooves. The third vent is provided at the center of the impellers, which matches with the central shaft of the thruster. The third hub of the impellers is supported on the second hub of the thruster. The central shaft of the thruster is coupled inside the third vent of the impellers. The retaining rings are mounted on the outer ring of the impellers and thruster. The end cover is fitted on the impellers. A sealed water flow passage is formed among the end cover's vent, the first division groove of the thruster, the second division groove of the impellers and the retaining ring. The end cover and thruster are installed together between the two neighboring impeller assemblies. A sealed water flow passage is formed between the impeller assemblies. The major difference between this technical plan and the existing submersible water pump for deep well operation lies in the structure of the impeller assemblies. During pumping water, impeller shaft rotates together with the motor shaft so as to drive thruster fixed on the impeller shaft to rotate, while the impeller shaft drives the thruster fixed on the impeller shaft to rotate. Impellers of the impeller assemblies, retaining rings and end cover rotate irregularly under the action of the thruster, thus forming a helical separation propelling mode, increasing water pressure, and making water supply distance longer, lift high and volume small. So it is unnecessary to install a fire fighting pump at a certain height, it is only to pull the water hose to the needed position. Install is fast, convenient, not limited by landform and has a wide applicable field, so it can meet fire fighting need.

As a modification, the first positioning ring is equipped in the direction of the first hub reverse to the outer periphery along the small end of thruster's first hub. The first positioning ring is fitted inside the first vent of the end cover and matches the first vent, thus facilitating the assembly.

As a modification, the second positioning ring is fitted in the direction of small end of the fourth hub facing the big end of the outer periphery along the fourth hub of the impellers. The first step is fitted on the second positioning ring. The inner periphery of the retaining ring matches the outer periphery of the first step, thus facilitating the assembly and sealing the water flow passage.

As a modification, the end cover is equipped with the third step and the fourth step. The outer periphery of the third step matches the inner periphery of the retaining ring; the outer periphery of the fourth step matches the inner periphery of the second positioning ring, thus facilitating the assembly and sealing the water flow passage.

As a modification, the maximum outer diameters of the end cover, retaining ring and the second positioning ring are equal, thus facilitating to put them into the pump housing.

As a modification, the stage of the described impeller assemblies is 30˜74, and the number of thruster's first blades is 3˜12, thus making single pump's water transmitting distance/lift reach 2500 m/100 m˜1500 m/200 m.

The first hub and the second hub of the thruster are of an open and diplex umbrella type. The first hub is in parallel with the second hub. The third hub and the fourth hub of the impellers are of an open and diplex umbrella type, and the third hub is in parallel with the fourth hub. Such shape is conducive to increasing water pressure. A rubber washer is fitted between the third vent of impellers and the central shaft of the thruster, which can reduce friction and mutual collision between the central shaft of thruster and impellers, thus enabling the fire fighting pump to be endurable.

As a modification, the first hub's maximum outer diameter is greater than the second hub's maximum outer diameter, the fourth hub's maximum outer diameter is greater than the third hub's maximum outer diameter, and the maximum outer diameters of the second hub and the third hub are basically the same, so it is convenient for smooth water flow, thus increasing fire fighting pump's water transmitting distance and lift. The helical direction of the first blade is reverse to that of the second blade.

As a further modification, pump housing is cylindrical for convenience of production. Thruster, impellers, end cover and retaining rings are made of stainless steel. So it improves wear resistance and tightness, and has a low requirement for water quality. Not like plastic material, stainless steel material will not produce deformation during high speed rotation, so pump body can be laterally, obliquely and vertically placed, and it suits various water qualities.

It is a kind of operating method of a fire fighting pump. Fire fighting pump includes a pump housing, a motor mounted inside the pump housing, and 2-stage or over 2-stage series-mounted impeller assemblies. Pump housing between the motor and impeller assemblies is equipped with a water inlet. Impeller assemblies are coaxially series-mounted on the impeller shaft. Impeller shaft is fixed on the motor shaft or coaxial with the motor shaft. Impeller assembly includes the thruster, impellers and end cover. Around the thruster and impellers are equipped with retaining rings. The first blades are provided on the thruster. The second blades are provided on the impellers, whose number is the same as that of the first blades and with the corresponding positions. Thruster is fixed on the impeller shaft. Impellers are coupled on the impeller shaft, and end cover passes through the impeller shaft. During pumping water, operating process includes that impeller shaft rotates together with the motor shaft. Impeller shaft drives the thruster fixed on the impeller shaft to rotate. Impellers, retaining ring and end cover of the impeller assemblies rotate irregularly under the action of the thruster. Operating way of a fire fighting pump forms a helical separation propelling mode that increases the water pressure, makes water supply distance longer and lift high, so it can meet fire fighting need.

Effective result of this invention derives from introduction of submersible water pump structure for deep well operation, increase of a thruster, so it forms a helical separation propelling mode and increases propelling water pressure, thus making water supply distance longer, lift high and easy water suction. Single pump water transmitting distance/lift can reach 2500 m/50 m˜1000 m/200 m while water pump's effective water supply flow/lift can reach 6.0 m/50 m˜3.0 m/2000 m per hour. It features small volume, quick and easy installation, no landform restriction and wide application field. Thruster and impellers are made of stainless steel material, so it increases its wear and tightness. It has a low water quality requirement. Not like plastic material, stainless steel material will not produce deformation during high speed rotation, so pump body can be laterally, obliquely and vertically placed, and it suits various water qualities.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic one for the submersible water pump of this invention to connect with outer equipments.

FIG. 2 is a schematic one for impeller assembly structure of the submersible water pump of this invention, which is cut along the central position of the assembly.

FIG. 3 is a dimensional resolution schematic one of this invention for an impeller assembly that is turned by 180°.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Concrete Implementation Mode

As shown in FIG. 1 to FIG. 3, a kind of fire fighting pump 29 includes a cylindrical stainless steel pump housing 1, a motor (not shown) fitted inside the pump housing 1 and 52-stage series-mounted impellers assemblies 30. A water inlet 31 is provided on pump housing 1 between the motor and impeller assembly 30 that is coaxially series-mounted on the impeller shaft 2. The impeller shaft 2 is an external hexagonal metal shaft and fixed on motor shaft (not shown) by means of a coupling and coaxially interacts with the motor shaft.

Impeller assembly 30 includes stainless steel end cover 3, stainless steel thruster 4, stainless steel impeller 5 and stainless steel retaining ring 6.

Thruster 4 includes central shaft 7, 3 first blades 8, the first hub 9 and the second hub 10. Thruster 4's first hub 9 and second hub 10 are of open diplex umbrella type. The first hub 9 and the second hub 10 are in parallel. The first hub 9's maximum outer diameter is greater than the second hub 10's maximum outer diameter. The first blade 8 is placed between the first hub 9 and the second hub 10. Three first division grooves 11 are formed among the first hub 9, the first blade 8 and the second hub 10. The second vent 12 that matches impeller shaft 2 is fitted on the central shaft 7. The second vent 12 is of an internal hexagonal type. Thruster 4 is fixed on impeller shaft 2 via the second vent 12. The first positioning ring 13 is provided in the direction reverse to the first hub 9 along the outer periphery of small end of thruster 4's first hub 9.

Impeller 5 includes the second blade 14 that is the same as the first blade 8. Positions of the third hub 15, the fourth hub 16 and the second blade 14 correspond to the position of the first blade 8. Impellers 5's third hub 15 and fourth hub 16 are of an open and diplex umbrella type. The third hub 15 and the fourth hub 16 are in parallel. Third hub 15's maximum outer diameter is smaller than the maximum outer diameter of the fourth hub 16. The second blade 14 is placed between the third hub 15 and the fourth hub 16. The second division groove 17 is formed among the third hub 15, the second blade 14 and the fourth hub 16, which is the same as the first division groove 11. The third vent 18 is provided in the center of the impeller, which matches the central shaft 7 of the thruster 4. A rubber washer 19 is fixed inside the third vent 18 of the impeller 5. The second positioning ring 20 is fitted in the direction of small end of the fourth hub 16 facing the big end of the outer periphery along the fourth hub of the impeller. The first step 21 is provided on the second positioning ring 20. The inner periphery of the retaining ring 6 matches the outer periphery of the first step 21.

The first vent 22 is provided on the center of the end cover 3. The first positioning ring 13 is fitted inside the first vent 22 of the end cover 3, and matches the first vent 22. End cover 3 is equipped with the third step 23 and the fourth step 24. The outer periphery of the third step 23 matches the inner periphery of the retaining ring 6 wile the outer periphery of the fourth step 24 matches the inner periphery of the second positioning ring 20.

Maximum outer diameters of the end cover 3 while retaining ring 6 and the second positioning ring 20 are equal. Maximum outer diameters of the second hub 10 and the third hub 15 are basically the same. The helical direction of the first blade 8 is reverse to that of the second blade 14.

Rubber washer 19 is fixed inside the third vent of the impeller. The central shaft 7 of the thruster 4 is mounted onto the rubber washer 19 of impeller 5. The third hub 15 of impeller 5 is supported on the second hub 10 of thruster 4. Retaining ring 6 is fitted on the outer periphery of impeller 5 and thruster 4, and matches the first step 21 of impeller 5. Central shaft 7 of thruster 4 is fixed on impeller shaft 2. Impeller 5 is coupled on the central shaft 7 of thruster 4 by means of rubber washer 19. Thruster 4 of neighboring impeller assembly 30 is mounted together with end cover 3. Outer periphery of the fourth step 24 of end cover 3 matches inner periphery of the second positioning ring 20 of impeller 5. A sealed water flow passage is formed among the end cover 3's vent, thruster 4's first division groove 11, impeller 5's second division groove 17 and retaining ring 6 while a sealed water flow passage is formed between impeller assemblies 30.

Submersible water pump's motor connects with generator 32. One end of impeller assembly 30 of the submersible water pump connects with water hose 33 that connects with water gun 34. Number of the first blades is 3. Submersible water pump introduces a 52-stage impeller assembly, a fire fighting water hose of 1.5 inch and 1200 m long for water transmission and 3 water operating hoses. Spray gun's nozzle diameter is 15 mm. There is one gun nozzle. Measured by satellite positioner, lift from the last water outlet position to the water level is 200 m, water outflow is 3.2 m3/h and spraying distance is 10 m, so it can meet fire fighting need.

Operating process of fire fighting pump 29 includes:

Motor shaft is driven to rotate by the motor Impeller shaft 2 rotates together with the motor shaft. Thruster 4 fixed on impeller shaft 2 rotates. Impeller assembly 30's impeller 5, retaining ring 6 and end cover 3 rotate irregularly under the action of thruster 4, thus forming a helical separation mode, increasing water pressure, making water supply distance longer, lift high and volume small so it is unnecessary to install a fire fighting pump 29 at a certain height, it is only to pull the hose to a needed position, installation is quick, simple, not limited by landform and has a wide application filed, and it can meet fire fighting need.

After survey of landform, operation of remote water pump includes:

(1) Install equipments: Connect generator 32 and water pump's power cable, connect water pump's outlet with hose 33 and place water pump into the water; (2) Turn on the machine: Start generator 32 with a key, turn on the controller of output power switch, operate the controller to start the water pump and pump water to put out the fire; (3) Turn off the machine: Operate the controller to stop the pump, turn off the controller, turn off the generator 32 with a key; (4) Take back equipments: Turn on water relief valve to drain water, disconnect hose 33 from water pump outlet, take out water pump from water, disconnect power cables of generator 32 and water pump and take back hose 33.

Precautions for operating remote water pump: (1) Check power cable for damage so as to prevent electric leakage; (2) Probe road and prepare a laying path before laying water hose 33 so as to have a smooth laying of hose; (3) Turn on and turn off the machine strictly according to procedures, otherwise it would affect lifetime of the equipments; (4) It should turn on the water relief valve before removing hose 33, which can be turned off only after water inside hose 33 is completely drained.

Application Example 2

What differs from application example 1 is that number of the first blades is 6. Submersible water pump introduces a 52-stage impeller assembly, a fire fighting water hose of 1.5 inch and 1200 m long for water transmission and 3 water operating hoses. Spray gun's nozzle diameter is 15 mm. There is one gun nozzle. Measured by satellite positioner, lift from the last water outlet position to the water level is 170 m, water outflow is 3.2 m3/h and spraying distance is 7.5 m, so it can meet fire fighting need.

Application Example 3

What differs from application example 2 is that number of the first blades is 5. Submersible water pump introduces a fire fighting water hose of 1.5 inch and 1200 m long for water transmission and one water operating hose. Spray gun's nozzle diameter is 5 mm. There is one gun nozzle. Measured by satellite positioner, lift from the last water outlet position to the water level is 200 m, water outflow is 3.0 m3/h and spraying distance is 10 m, so it can meet fire fighting need.

Application Example 4

What differs from application example 2 is that number of the first blades is 7. Submersible water pump introduces a fire fighting water hose 33 of 10 inch and 140 m long for water transmission and 3 water operating hose. Spray gun's nozzle diameter is 3 mm. There are 2 gun nozzles. Measured by satellite positioner, lift from the last water outlet position to the water level is 200 m, water outflow is 3.0 m3/h and spraying distance is 10 m, so it can meet fire fighting need.

Application Example 5

What differs from application example 2 is that number of the first blades is 9. Submersible water pump introduces a 30-stage impeller assembly and fire fighting water hose of 1.5 inch and 1200 m long for water transmission and one water operating hose. Spray gun's nozzle diameter is 15 mm. There is one gun nozzle. Measured by satellite positioner, lift from the last water outlet position to the water level is 50 m, water outflow is 2.2 m3/h and spraying distance is 4 m, so it can meet fire fighting need.

Application Example 6

What differs from application example 2 is impeller assembly 30 includes plastic end cover 3, plastic thruster 4, plastic impeller 5 and plastic retaining ring 6. The number of the first blades is 12. Submersible water pump introduces a 75-stage impeller assembly and fire fighting water hose of 1.0 inch and 1250 m long for water transmission and 2 water operating hoses. Spray gun's nozzle diameter is 15 mm. There is one gun nozzle. Measured by satellite positioner, lift from the last water outlet position to the water level is 50 m, water outflow is 2.2 m3/h and spraying distance is 4 m, so it can meet fire fighting need. 

1. A fire pump comprising a pump housing, a motor fitted inside the pump housing, and series-mounted impeller assemblies of 2-stage or over 2-stage that are fitted inside the cylindrical cavity of the pump housing, a water inlet being provided on the pump housing between motor and impeller assembly, impeller assemblies being coaxially series-mounted on the impeller shaft, impeller shaft being fixed on the motor shaft or shares motor shaft, characterized in that the impeller assembly includes end cover, thruster, impeller and retaining rings, the first vent is provided in the center of the end cover, the thruster includes the central shaft, 3 or more than 3 first blades, the first hub and the second hub, the first blades are placed between the first hub and the second hub. 3 or more than 3 first division grooves are formed among the first hub, the first blades and the second hub, inside the central shaft is the second vent that matches the impeller shaft, the thruster is fixed on the impeller shaft via the second vent, the impeller includes the second blades whose number is the same as those of the first blades, the positions of the third hub, the fourth hub and the second blades correspond with the position of the first blades, the second blades are placed between the third hub and the fourth hub, the second division grooves are formed among the third hub, the second blades and the fourth hub, whose groove number is the same as those of the first division grooves, the third vent that matches the central shaft of the thruster is provided in the center of the impeller, the third hub of the impeller is supported on thruster's second hub while thruster's central shaft is coupled inside impeller's third vent, retaining rings are fitted on the outer peripheries of the impeller and thruster, end cover is mounted on the impeller, a sealed water flow passage is formed among the end cover's vent, the first division groove of the thruster, the second division groove of the impellers and the retaining rings, the end cover and thruster are installed together between the two neighboring impeller assemblies, and a sealed water flow passage is formed between the impeller assemblies.
 2. The fire pump as claimed in claim 1, wherein the first positioning ring is equipped in the direction of the first hub reverse to the outer periphery along the small end of thruster's first hub. The first positioning ring is fitted inside the first vent of the end cover and matches the first vent.
 3. The fire pump as claimed in claim 2, wherein that the second positioning ring is fitted in the direction of small end of the fourth hub facing the big end of the outer periphery along the fourth hub of the impellers. The first step is fitted on the second positioning ring. The inner periphery of the retaining ring matches the outer periphery of the first step.
 4. The fire pump as claimed in claim 3, wherein the third step and the fourth step are provided on the end cover, the outer periphery of the third step matches the inner periphery of the retaining ring, and the outer periphery of the fourth step matches the inner periphery of the second positioning ring.
 5. The fire pump as claimed in claim 4, wherein the maximum outer diameters of the end cover, retaining ring and the second positioning ring are equal.
 6. The fire pump as claimed in claim 5, wherein the number of stages of the described impeller assembly is 30˜74 while the number of the first blades of the described thruster is 3˜12.
 7. The fire pump as claimed in claim 6, wherein the first hub and the second hub of the thruster are of open and diplex umbrella type, the first hub and the second hub are in parallel; the third hub and the fourth hub of the impeller are of open and diplex umbrella type, and the third hub and the fourth hub are in parallel. A rubber ring is fitted between the third vent of the impeller and the central shaft of the thruster.
 8. The fire pump as claimed in claim 7, wherein the maximum outer diameter of the first hub is greater than the maximum outer diameter of the second hub, the maximum outer diameter of the fourth hub is greater than the maximum outer diameter of the third hub, while the maximum outer diameters of the second hub and the third hub are basically the same, and helical direction of the first blade is reverse to that of the second blade.
 9. The fire pump as claimed in claim 8, wherein the described pump housing is of cylindrical shape and the described end cover, thruster, impeller and retaining ring are made of stainless steel material.
 10. An operating method of a fire pump, wherein the fire pump includes a pump housing, a motor installed inside the pump housing, and 2-stage or over 2-stage series-mounted impeller assemblies installed inside the cylindrical cavity of the pump housing, a water inlet is provided on the pump housing between the motor and the impeller assembly and impeller assembly is coaxially series-mounted on the impeller shaft, impeller shaft is fixed on the motor shaft or shares motor shaft, characterized in that the described impeller assembly includes the thruster, impeller and end cover, around the thruster and impeller are equipped with retaining rings, thruster is equipped with the first blades, impeller is equipped with the second blades whose number is the same as that of the first blades, but with corresponding positions, thruster is fixed on the impeller shaft while impeller is coupled on the impeller shaft, end cover passes through the impeller shaft, during pumping water, operating process includes that impeller shaft rotates together with the motor shaft, impeller shaft drives the thruster fixed on the impeller shaft to rotate, impellers, retaining rings and end cover of the impeller assemblies rotate irregularly under the action of the thruster. 